Sprague-Dawley rats treated with a thiamine deficient diet develop a syndrome that behaviorally and neuropathologically resembles Wernicke's encephalopathy (the acute phase of Korsakoff's psychosis). Preterminal rats (approximately 50% weight of control animals) improve behaviorally within hours after intraperitoneal injection of thaimine and after 2-3 months weigh the same appear no different from control animals. The duration of thiamine deficiency required to reach the preterminal state varies greatly. The percent weight gain 1 day after thiamine injection was correlated with the duration of thiamine deficiency. Serotonin turnover was augmented in acutely ill animals compared to controls in several brain regions examined but was no different seven months afterwards. However, recovered animals (7 months post-thiamine deficiency) became significantly more intoxicated, developed a greater decrease in body temperature, and about 20% died after alcohol administration.